Kōji is a supporting character in Time of Eve who appears as a regular patron of the café of the same name. He is later revealed to be an android, though this fact is not immediately obvious to the other customers, including his own partner. Kōji is a quiet and seemingly honest young man with a simple demeanour. He often appears absentminded and carries a camera with him at all times, indicating a keen interest in photography and a particular attention to the equipment he uses. His reserved nature makes him somewhat hard to read at first, but he interacts warmly with those he trusts.

His primary motivation centers on his relationship with Rina, a young woman he believes to be human. The two are always together and are perceived by others as a somewhat unbalanced couple, with Kōji often taking a more passive or contemplative role. In truth, both Kōji and Rina are androids, each unaware of the other's true identity. This mutual misunderstanding forms the core of their storyline and serves to explore the café's central theme of non-discrimination between humans and androids. Kōji's role in the narrative is to illustrate the complexity of android emotions and the ease with which appearances can deceive; his genuine affection for Rina exists within the boundaries of Asimov's Three Laws, yet it feels no less authentic for being programmed.

Throughout the series, Kōji's character does not undergo dramatic transformation, but his presence contributes to the gradual revelation that many café regulars are androids living out human-like experiences. His development lies in the quiet acceptance of his own nature and the deepening of his bond with Rina. Notable abilities are limited to his photographic skill and his gentle observational eye, which mirror his quiet personality. Kōji ultimately embodies the ambiguity at the heart of Time of Eve: the distinction between human and android is less important than the connections they form.